1. Field of the Invention
The present invention relates generally to casting and more particularly to an article having a pattern which is to be incorporated into the bonding surface of an appliance during its manufacture by investment casting and its method of incorporation.
2. Description of the Prior Art
The present invention is applicable to the casting of metallic appliances or devices requiring a surface which facilitates bonding by an adhesive, and is particularly suitable to the manufacture of dental appliances.
Bonding of intraoral dental appliances to the surfaces of teeth is frequently necessary during orthodontic treatment. Proper bonding with an adhesive necessitates the preparation of both the bonding surface of the appliance and the tooth surface. Conventionally, the tooth enamel is acid etched to enhance the bonding of the adhesive to the tooth. The bonding surface of an orthodontic appliance may be prepared by attaching a porous mesh bonding pad to the appliance by brazing, welding or sintering.
The surface of a cast dental appliance may be electrolytically etched. This approach is used in what has become known as the Maryland Bridge technique, popularized by Drs. Thompson and Livaditis at the University of Maryland. The Maryland Bridge typically consists of a central pontic with wing-like retainers at each end for attachment to abutment teeth. The bonding surface of the Maryland Bridge retainers are acid etched to create an irregular surface which increases its bondability to the surface of a tooth. In contrast with the earlier and traditional crown and bridge techniques the two abutment teeth, one on each of the opposite sides of the pontic, are not ground down, and the need for a partial denture is eliminated.
Disadvantages of the Maryland Bridge technique are that only the less corrosion resistant base metal alloys can be satisfactorily etched, and the etching process is itself difficult to control as the extent and evenness of the etch are dependent on the current, voltage, surface area and acid strength.
Problems that dental laboratories are faced with when practicing this technique involve the use of acids. Some dental laboratories are unaccustomed to using corrosive acids in their routine operation and such fluids may cause accidents. In addition, acid fumes require suitable exhaust ventilation, e.g. a chemical fume hood, which may be lacking in many smaller laboratories. A further drawback is that the equipment for etching is expensive, as it includes at a minimum an electroplating device with a stirrer and timer.
It is a primary object of the present invention to simplify the manufacture of an appliance having a bonding surface with irregularities, without using acid etching or the addition of a bonding pad to the cast article.
It is another object of the present invention to cast an appliance as a single element with a plurality of irregularities formed into the tooth abutting surface of the appliance.
It is also an object of the present invention to provide a preformed pad which is beneficially incorporated into a mold to form a patterned bonding surface.
It is a further object of the present invention to provide a device capable of producing a patterned bonding surface in corrosion resistant alloys, as well as etchable metallic alloys.
It is an additional object to provide a patterned bonding surface to an orthodontic appliance which achieves greater bonding strength with tooth enamel than devices presently available.
It is also an object of the present invention to simplify and reduce the time necessary for the fabrication of a dental bridge.